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I have a 2006 X3 with 70K miles. High-pitched fast-paced chattering just started - sounds like it's coming from rear driver-side exhaust area. When the car "warms up", it goes away. After 5 min off, and restart - same issue, but again - goes away after running for a bit. any ideas?

py, the "butterfly" valve sounds like it might be the source. You have a fair amount of milage and I suspect all that hot exhaust has taken its toll on the valve. There were a number of posts about the valve much earlier, and something called a golf tee modification that was suggested for a better exhaust sound.

py, the "butterfly" valve sounds like it might be the source. You have a fair amount of milage and I suspect all that hot exhaust has taken its toll on the valve. There were a number of posts about the valve much earlier, and something called a golf tee modification that was suggested for a better exhaust sound.

+1. The valve in #2 tailpipe is sucked shut under vacuum and opens under load.

The mod was to remove the pipe providing the suction (i.e. the valve stays open) and plug it with a golf tee and zip tie it out of the way.

Ours is being driven like a Madwoman by Mrs. Wingspan at the moment (just kidding, she is at work) or I would go peer at the exhaust and see.

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“Character is doing the right thing when nobody’s looking. There are too many people who think that the only thing that’s right is to get by, and the only thing that’s wrong is to get caught.”

An even easier way to do the mod is to open the rear driver's side cargo panel and there is a vacuum servo there. Remove the tubing coming off the side and cap the outlet on the servo with a 1/8 vacuum cap. That's it.